Swayback in horses, known clinically as lordosis, happens when the ligaments and muscles supporting the spine weaken and allow the back to dip downward. The most common cause is simple aging, but genetics, repeated pregnancies, and congenital vertebral malformations can also play a role. Some horses are born with a predisposition to it, while others develop it gradually over years of wear.
How Aging Weakens the Spine
The most frequent cause of swayback is age-related deterioration. A horse’s vertebral column is held in place by a network of ligaments running along the top of the spine, supported from below by the abdominal muscles. As a horse ages, those ligaments lose elasticity and strength. At the same time, the abdominal muscles weaken, and the added weight of a sagging belly pulls the spine downward. The result is the characteristic U-shaped dip through the back.
This process is gradual. Most owners notice it developing in horses over 15 to 20 years old, and it tends to worsen slowly over time. Broodmares that have carried many foals are especially prone because repeated pregnancies stretch and weaken the abdominal wall, removing a key source of spinal support.
The Genetic Component
Not all swayback is age-related. Some horses develop a noticeable dip in their backs at a young age, and research points to a strong genetic basis for this early-onset form. A genome-wide study of American Saddlebred horses identified a specific region on chromosome 20 associated with congenital lordosis. Among 33 affected horses, 80% were homozygous (carrying two copies) of the linked genetic variant, compared to just 15% of unaffected horses. The difference was highly significant statistically, suggesting a major gene with a recessive inheritance pattern, meaning a horse typically needs to inherit the variant from both parents to be affected.
About 5% of American Saddlebreds in one study met the threshold for swayback. The condition also appears at notable rates in other breeds, including Arabians, Quarter Horses, and Peruvian Pasos. Researchers have not yet identified the exact gene responsible, though the candidate region on chromosome 20 contains over 50 known and predicted genes.
Congenital Vertebral Malformations
In rarer cases, swayback stems from structural abnormalities in the vertebrae themselves. Postmortem imaging of affected horses has revealed malformed vertebral bodies in the thoracic spine (roughly the area beneath the saddle), partial fusion of vertebrae, abnormal spinous processes, and malformed ribs with degenerative changes at the joints where ribs meet the spine. These congenital defects alter the normal alignment of the vertebral column and can produce visible curvature from a young age, sometimes accompanied by scoliosis (side-to-side curvature) in addition to the downward dip.
Does Swayback Cause Pain?
Many horse owners wonder whether a swaybacked horse is uncomfortable or simply looks different. The answer depends on the individual horse. Back pain in horses commonly shows up as poor hindlimb impulsion, muscle spasm when the back is touched, resistance to bending laterally, and overall stiffness through the back muscles. Horses with back pain typically respond to digital pressure along the spine. Interestingly, lameness is not a major feature. In clinical assessments, very few horses with confirmed back pain showed outright lameness, suggesting that what looks like a gait problem may actually be the horse shifting its weight to accommodate spinal discomfort rather than favoring a sore leg.
A mild swayback in an older horse that moves freely and shows no pain response to palpation is often more cosmetic than clinical. A pronounced dip, especially one that developed quickly or in a younger horse, warrants closer evaluation.
Maintaining Muscle Mass With Nutrition
Adequate protein intake is essential for preserving the muscle that supports a horse’s topline. Research on mature horses found that muscle-building pathways respond in a dose-dependent way to dietary protein: feeding approximately 0.25 grams of crude protein per kilogram of body weight per meal produced near-maximal activation of muscle protein synthesis. Doubling that amount to 0.5 grams per kilogram did not produce any additional benefit, indicating a clear plateau.
For a 500-kilogram (1,100-pound) horse, that translates to roughly 125 grams of protein per meal from a quality protein source. This matters most for senior horses already losing muscle along the back and hindquarters. Simply adding more and more protein beyond the effective threshold does not help and can trigger metabolic resistance that actually reduces the body’s ability to build muscle. The quality and timing of protein matter as much as the quantity.
Strengthening Exercises for the Back
Core-strengthening exercises can slow the progression of swayback and, in some cases, partially restore topline muscle. Belly lifts are the most widely used technique, essentially the horse equivalent of abdominal crunches. They work by triggering the horse to contract its abdominal muscles and round its back upward.
There are two common methods. The first uses upward finger pressure at the girth area to stimulate a lift. The second uses finger pressure at the croup: you press your fingertips into the grooves on either side of the croup and run them downward, prompting the horse to tuck its pelvis and hunch its back. As soon as the horse tucks, you release the pressure. Five repetitions per session is a standard starting point, and most horses learn to respond quickly.
Ridden and in-hand work over ground poles, hill work, and transitions that encourage the horse to step under itself with the hind legs also build the muscles along the topline. Consistency matters more than intensity, especially with older horses.
Saddle Fitting for a Swaybacked Horse
A standard saddle placed on a swaybacked horse will “bridge,” meaning the panels make contact at the front and back but hover over the dipped middle section. This concentrates pressure on two small areas instead of distributing it evenly, which can cause soreness and make the problem worse.
The most effective solution is a saddle pad with an open shimming system that lets you place shims of varying thickness exactly where the gap exists. Closed-pocket pads or pads with bridging shims sewn in at fixed positions can actually cause more harm if the placement or thickness doesn’t match your horse’s specific back shape.
Start with the thinnest shim possible. If the saddle still bridges, add a second layer. Over-shimming creates new pressure points and can worsen the swayback over time. The goal is to use fewer shims as the horse’s back muscles strengthen, not to keep adding material. For horses with only a minor dip, a high-quality shock-absorbing pad alone may provide enough fill to eliminate bridging. Shims can also be trimmed with scissors for a custom fit in horses with asymmetrical dips.